Scalar dark matter with Z3 symmetry in the type-II seesaw mechanism

We study a simple complex scalar singlet dark matter (DM) model with Z3 symmetry in the framework of the type-II seesaw mechanism. We use the model to explain the excess of electron-positron flux measured by the AMS-02, DAMPE, and Fermi-LAT Collaborations, which is encouraged by the decay of the triplets produced from dark matter annihilations in the Galactic halo. We focus on the nondegenerate case in which the mass of DM is larger than that of the triplets' and deliberately alleviates the leptophilic properties of the DM, so that the semiannihilation effects are enhanced. With the guarantee of Z3 symmetry, by fitting the antiproton spectrum observed in the PAMELA and AMS experiments, we find that the DM cubic terms and the couplings between DM and the Higgs boson are strongly constrained, leading to the semiannihilation cross-section fraction less than 11% when DM mass is given at 2 TeV.